1. Field of the Invention
The present invention relates to an input device that inputs information according to a state of proximity of an object using a change in capacitance or the like, and a method and a program for controlling the input device, and particularly, to an input device that inputs information according to an operation of a finger, a pen, or the like in various information devices such as a computer.
2. Description of the Related Art
Since a sensor that detects a change in capacitance can detect the proximity of an object (for example, a finger or a pen) with a simple configuration, the sensor has been widely used for user interface devices of various electronic devices, such as a touch pad of a notebook computer or a touch panel of a smart phone.
In Japanese Unexamined Patent Application Publication No. 2010-244132, a user interface device that determines a state of proximity of an object to a touch panel using a detection signal output from a capacitive touch panel is described. This user interface device determines whether the object in proximity to the touch panel is a finger or a palm, and selects an application to be executed, based on a result of the determination and coordinates of a proximity position on the touch panel.
In Japanese Unexamined Patent Application Publication No. 2010-244132 above, a method of using a positional distribution of a capacitance change is described as a method of determining whether the object in proximity to the touch panel is a finger or a palm. In this method, the object is determined to be a finger when a mountain of the distribution of the capacitance change is relatively steep, and the object is determined to be a palm when the mountain is relatively gentle.
However, how to evaluate the steepness of the mountain of the distribution is not specifically described in Japanese Unexamined Patent Application Publication No. 2010-244132. For example, a method of evaluating the steepness by examining a frequency spectrum of a distribution curve is considered. However, in this method, there are problems in that an amount of calculation increases, and a processing time becomes long.
Further, in Japanese Unexamined Patent Application Publication No. 2010-244132, another method of discriminating between a finger and a palm includes a method of counting the number of sensor electrodes in which a change in capacitance greater than a predetermined threshold value is detected. The counted value indicates the width of a contact region of the object. A finger is determined to come in contact when the counted value is smaller than the predetermined threshold value, and a palm is determined to come in contact when the count value is greater than the predetermined threshold value.
However, in this method, when the threshold value for determination is set to be low, the difference between the finger and the palm becomes small in the counted value, and accordingly, there is a problem in that discrimination between a finger and a palm becomes difficult. On the other hand, when the threshold value for determination is set to be high, there is a problem in that it is difficult to detect the contact of the object when the change in capacitance is small (for example, when the object makes weak contact).